An optical pickup is a device to read/write information using a spot formed by gathering laser light emitted from a laser diode (LD) with an object lens on a recording surface of a disc.
A general optical pickup mainly has three elements, i.e., an optical system, an object lens actuator and a circuit board. The optical system focuses the laser light emitted from the laser diode, and reads information on a disc utilizing the reflection light from the disc or writes information on a recording layer of the disc. The object lens actuator drives the object lens in a focusing direction and a tracking direction to align a focal point of the object lens on a track on the disc. The circuit board electrically connects the object lens actuator and the optical system with an external controller. These parts are fixed in a case (housing).
As the material of the case, a resin material, having molding workability corresponding to a complicated shape, appropriate to mass-production at a lower cost in comparison with a metal, is mainly used. In an optical pickup having a case made of a resin material, as the thermal conductivity of the case itself is low, a metal plate having high thermal conductivity is provided on the top panel side or bottom panel side of the case, and the metal plate is thermally connected with the laser diode. With this arrangement, the cooling capability for the laser diode is ensured.
In the optical pickup in which the metal plate is fixed to the case made of a resin material in this manner, when an environmental temperature has changed, the case may be distorted by thermal stress due to the difference of expansion and contraction amount between the parts. When the case is distorted, the optical parts attached to the case is inclined in accordance with the distortion of the case. The inclination of the optical parts may become a factor to change a focal distance and/or focal position and disturb stable read/write operations. Accordingly, it is necessary to suppress the distortion of the case.
Regarding the problem of the distortion of the case in accordance with change of environmental temperature, known is an optical pickup as disclosed in PTL1 (Japanese Patent Laid-open No. 2008-77699) where a metal plate is screw-fixed to a case in the vicinity of one of two bearings of the case and is fitted in between engagement claws of the case in the vicinity of the other bearing.
According to the above art, it is possible to swing the metal plate to some degree relatively to the case, with the screw as a center, and displace it in the bearing direction. The distortion of the case in accordance with temperature change can be suppressed. As a result, the position of the optical part provided in the case are maintained constant, and it is possible to perform stable read/write operation.
[Citation List]
[Patent Literature]
[PTL 1] Japanese Patent Laid-open No. 2008-77699 (claim 1, FIG. 5)